SCB-68 68-Pin Shielded Connector Block Installation Guide
Contents
1. Single Ended Inputs When measuring floating signal sources configure your MIO 16 board to supply a ground reference Therefore you should configure the MIO 16 for referenced single ended input In this configuration the negative input of the MIO 16 instrumentation amplifier is tied to the analog ground Therefore you should use the SCB 68 board in its factory configuration In the factory configuration jumpers are in the two series positions F and G see Figure 7 In this configuration you should tie all of the signal grounds to AIGND Connecting Ground Referenced Signal Sources A grounded signal source is connected in some way to the building system ground therefore the signal source is already connected to a common ground point with respect to the DAQ board assuming that the host computer is plugged into the same power system Nonisolated outputs of instruments and devices that plug into the building power system fall into this category SCB 68 Connector Block Installation Guide amp National Instruments Corporation Differential Inputs If the MIO 16 DAQ board is configured for differential inputs ground referenced signal sources connected to the SCB 68 board need no special components You can leave the inputs of the SCB 68 board in the factory configuration that is with the jumpers in the two series positions F and G see Figure 7 Single Ended Inputs When you measure ground referenced signals the external signal2. voltage dividers to the SCB 68 analog inputs Attenuators can reduce a signal that is outside the normal input range of the DAQ board 10 V maximum Warning The SCB 68 board is not designed for any input voltages greater than 42 V even if a user installed voltage divider reduces the voltage to within the input range of the DAQ board Input voltages greater than 42 V can damage the SCB 68 board any and all boards connected to it and the host computer Overvoltage can also cause an electric shock hazard for the operator National Instruments is NOT liable for damage or injury resulting from such misuse Single Ended Input Attenuators There is a two resistor circuit for attenuating voltages at the single ended inputs on the SCB 68 Install resistors in positions F and B for one channel and G and C for the next channel You can determine the gain G of this attenuator using the following formula G Rb Rb Rf or G Rg Rg Re Therefore the input to the MIO 16 board VM1o is computed as follows Volo Vsc G where Vsc is the voltage applied to the SCB 68 screw terminals The accuracy of this gain equation depends on the tolerances of the resistors you use Differential Input Attenuators There is a three resistor circuit for attenuating voltages at the differential inputs on the SCB 68 Use positions E F and G for the resistors SCB 68 Connector Block Installation Guide 10 National Instruments Corporation Use the followin
3. Typical 1 mA with no signal conditioning installed Maximum 800 mA from host computer Note The power specifications pertain to the power supply of the host computer when using internal power or to the external supply connected at the 5 V screw terminal when using external power The maximum power consumption of the SCB 68 is a function of the signal conditioning components installed and any circuits constructed on the general purpose breadboard area If the SCB 68 is being powered from the host computer the maximum 5 V current draw is fuse limited to 800 mA National Instruments Corporation 13 SCB 68 Connector Block Installation Guide Physical Box dimensions including box feet 7 7 by 6 0 by 1 8 in 19 5 by 15 2 by 4 5 cm T O connectors One 68 pin male SCSI connector Screw terminals 68 Operating Environment Temperature 0 to 70 C Relative humidity 5 to 90 noncondensing Storage Environment Temperature 55 to 125 C Relative humidity 5 to 90 noncondensing SCB 68 Connector Block Installation Guide 14 National Instruments Corporation
4. 68 board make adding signal conditioning components to the analog input signals easier Figure 7 shows an example for a specific input channel and all of the channels are arranged the same way Soldering and Desoldering on the SCB 68 Board Some applications discussed here require you to make modifications to the printed circuit board usually in the form of adding components The SCB 68 board is shipped with wire jumpers in the F and G positions see Figure 7 you must remove them to use the positions Use a low wattage soldering iron 20 to 30 W when soldering to the board To desolder on the SCB 68 vacuum type tools work best Be careful to avoid damaging the component pads when desoldering Use only rosin core electronic grade solder because acid core solder damages the printed circuit board and components Figure 7 Channel Configuration Diagram National Instruments Corporation 7 SCB 68 Connector Block Installation Guide Channel Configurations You can configure the analog input channels of an MIO 16 board for one of three input modes differential referenced single ended or nonreferenced single ended These modes are called DIFF RSE and NRSE input modes respectively As described in your MIO 16 user manual the input configuration of the MIO 16 board depends on the type of signal source you are using There are two types of signal sources nonreferenced or floating signals and ground referenced signals To measur
5. 80 gt 59000000000020 0000000006 25000000000054 0000000000 580000000000 000000000 28888888888 oc 0000000000 0000000000 EETA 0000000000 o V Breadboard Area Product Name Cold Junction Compensation Temperature Sensor SO eaee Fuse 0 8 A Switches S1 and S2 ee pelo Assembly Number and Revision Letter GABA 10 02 eSlaAssy 8 He Screw Terminals aca Serial Number RC Filters and Attenuators for DACO DAC1 and Ext Trig Figure 2 SCB 68 Board Parts Locator Diagram National Instruments Corporation 3 SCB 68 Connector Block Installation Guide Switch Settings and Temperature Sensor Configuration To accommodate thermocouples with the AT MIO 16X and MIO 16E Series boards the SCB 68 connector block has a temperature sensor for cold junction compensation To power the temperature sensor set switches S1 S2 and S3 as shown in Figures 3 4 and 5 Notice that this also turns the signal conditioning accessory power on accessories can include temperature sensors and signal conditioning circuitry You can configure the temperature sensor as follows e For single ended operation connect referenced single ended analog channel 0 to the temperature sensor by switching S5 to the up position The signal is referenced to analog input ground Set the switches as shown in Figure 3 Figure 3 Single Ended Switch Configuration e For differential operation connect different
6. A fuse Pin 14 is also 5 V and is not fuse protected on the SCB 68 Shorting pin 14 to ground will blow the MIO fuse which is usually socketed If the SBC 68 does not work when you turn the DAQ board on first check the switch settings then check both the 800 mA fuse on the SCB 68 board and the output fuse if any on the DAQ board Before replacing any fuses check for short circuits from power to ground The 5 V power on the SCB 68 is filtered with a 470 Q series resistor R21 as the filtered 5 V is loaded the voltage decreases Pad R20 is in parallel with R21 and you can install a resistor if needed Shorting R20 bypasses the filter while capacitatively coupling DGND and AGND and is not recommended National Instruments Corporation 5 SCB 68 Connector Block Installation Guide Quick Reference Label A quick reference label is in your kit for your convenience This label shows the switch configurations and defines the screw terminal pinouts for the AT MIO 16X and MIO 16E Series boards You can put the label on the inside of the SCB 68 cover for easy reference Signal Connection The following warnings contain important safety information concerning hazardous voltages and terminal blocks Warnings KEEP AWAY FROM LIVE CIRCUITS Do not remove equipment covers or shields unless you are trained to do so If signal wires are connected to the module or terminal block dangerous voltages may exist even when the equipment is turned off To a
7. INSTRUMENTS Connector Block The Software is the Instrument Wy NATIONAL SCB 68 68 Pin Shielded p Installation Guide Part Number 320745 01 This guide describes how to connect and use the SCB 68 68 pin shielded connector block with National Instruments 68 pin products In addition to the SCB 68 kit contents you need Phillips head number 1 and number 2 screwdrivers a 0 125 in flathead screwdriver long nose pliers wire cutters and wire insulation strippers If you are adding components you also need a soldering iron and solder and resistors and capacitors specific to your application Introduction The SCB 68 is a shielded board with 68 screw terminals for easy connection to National Instruments 68 pin products When you use the SCB 68 with the AT MIO 16X or MIO 16E Series boards you can use the 16 screw terminals for signal connection to the 16 analog inputs There is a breadboard area for adding resistance capacitance RC filtering an attenuator 4 to 20 mA current sensing and open thermocouple detection There is also a cold junction temperature sensor for use with thermocouples When you are using an unmodified SCB 68 with other 68 pin products you can configure the five switches to give you a general purpose 68 screw terminal connector block The SCB 68 has a strain relief bar for securing signal wires or cables What Your Kit Should Contain The SCB 68 68 pin shielded connector block kit part number 776844 01 co
8. coefficient of a thermocouple is 32 UV C this measurement error adds 0 5 C of uncertainty to the measurement For best results you must use a well calibrated MIO 16 board so that offsets can be ignored You can eliminate offset error however by grounding one channel on the SCB 68 board and measuring the voltage You can then subtract this value the offset of the MIO 16 in software from all other readings Thermocouple wire error is the result of inconsistencies in the thermocouple manufacturing process These inconsistencies or nonhomogeneities are the result of defects or impurities in the thermocouple wire The errors vary widely depending on the thermocouple type and even the gauge of wire used but a value of 2 C is typical For more information on thermocouple wire errors and more specific data consult your thermocouple manufacturer For best results use the average of many readings about 100 or so typical absolute accuracies should then be about 2 C Specifications This section lists the SCB 68 specifications These ratings are typical at 25 C unless otherwise stated The operating temperature range for this board is 0 to 70 C Analog Input Number of channels Eight differential 16 single ended Cold junction sensor Accuracy 1 0 C over a 0 to 110 C range Output 10 mV C Other signals All other MIO 16 I O signals are available at screw terminals Power Requirement Power consumption at 5 VDC 5
9. e floating signal sources configure the MIO 16 for referenced single ended input or differential input with bias resistors To measure ground referenced signal sources configure the MIO 16 for nonreferenced single ended input or differential input Both types of signal sources and the recommended methods for MIO 16 board connection are discussed as follows Connecting Nonreferenced or Floating Signal Sources A floating signal source is a signal source that is not connected in any way to the building ground system but has an isolated ground reference point If an instrument or device has an isolated output that instrument or device falls into the floating signal source category Some examples of floating signal sources are outputs for thermocouples transformers battery powered devices optical isolators and isolation amplifiers The ground reference of a floating source must be tied to the ground of the DAQ board to establish a local or onboard reference for the signal Differential Inputs To provide a return path for the instrumentation amplifier bias currents floating sources must have a 10 to 100 kQ resistor to AIGND on one input if they are DC coupled or on both inputs if sources are AC coupled You can install bias resistors in positions B and D see Figure 7 of the SCB 68 For more detailed information on connections to floating signal sources and differential inputs refer to the configuration chapter in your MIO 16 board user manual
10. ection earlier in this guide Build open thermocouple detection circuitry by connecting a high value resistor between the positive input and 5 V The value of this resistor is relatively unimportant a few megohms or more works fine With a high value resistor you can detect an open or defective thermocouple If the thermocouple opens the voltage measured across the input terminals rises to 5 V a value much larger than any legitimate thermocouple voltage The 100 kQ resistor between the negative input and AIGND is a bias current return path as described in the Connecting Floating Signal Sources section earlier in this guide Differential Open Thermocouple Detection Use position A to connect a high value resistor between the positive input and 5 V Leave the jumpers in place positions F and G for each channel used Single Ended Open Thermocouple Detection Use position A for one channel and D for the next channel when you connect a high value resistor between the positive input and 5 V Leave the jumpers in place for each channel position F for one channel and G for the next channel National Instruments Corporation Il SCB 68 Connector Block Installation Guide RC Filters and Attenuators for DACOOUT DACIOUT and EXTTRIG You can connect RC filters and attenuators to the DACOOUT DACIOUT and EXTTRIG signals at the SCB 68 board RC filters can reduce noise You can build these using the SCB 68 pads Filtering increases settling time
11. ents Single Ended RC Filters You can build single RC filters using the pads F and B for one channel and G and D for the next channel Solder the resistor in position F or G and the capacitor in position B or D The following equation shows how to determine your cutoff frequency Fc and settling time depending on the resistors and capacitators you use Fe 1 2 RC Differential RC Filters You can build a differential RC filter using the pads F and E Solder the resistor in position F and the capacitor in position E The following equation shows how to determine your cutoff frequency Fc and settling time depending on the resistors and capacitators you use Fe 1 2 TRC National Instruments Corporation 9 SCB 68 Connector Block Installation Guide Using 4 to 20 mA Inputs You can connect a resistor to the analog inputs at the SCB 68 board for use with current sourcing devices You can perform single ended or differential sensing using the SCB 68 pads Accuracy depends on the resistor you use Never exceed 10 V at the analog inputs Single Ended Inputs Use position B for one channel and position C for the next channel Leave the jumpers in place for each channel position F for one and position G for the next Differential Inputs Use position E for each channel you are using for current sensing Leave the jumpers in positions F and G for each channel Building Attenuators Voltage Dividers You can connect attenuators
12. g equation to determine the sources of error G Re Re Rf Rg Therefore the input to the MIO 16 board Vo is computed as follows Volo Vsc G where Vsc is the voltage applied to the SCB 68 screw terminals The accuracy of this gain equation depends on the tolerances of the resistors you use Using the SCB 68 Board for Thermocouple Measurements The maximum voltage level thermocouples generate is typically a few millivolts Therefore you should use an MIO 16 with high gain for best resolution You can measure thermocouples in either differential or single ended configurations The differential configuration has better noise immunity but the single ended configuration has twice as many inputs The MIO 16 board must have a ground reference because thermocouples are floating signal sources Therefore you must use bias resistors if the board is in differential mode For single ended configuration use the referenced single ended input configuration Cold junction compensation with the SCB 68 board is accurate only if the temperature sensor reading is close to the actual temperature of the screw terminals When you are reading thermocouple measurements keep the SCB 68 board away from drafts or other temperature gradients such as those caused by heaters radiators fans and very warm equipment Input Filtering and Open Thermocouple Detection Optional To reduce noise you can connect a lowpass filter Refer to the Building RC Filters s
13. hermocouple measurements with the SCB 68 board and an MIO 16 board the possible sources of error are compensation linearization measurement and thermocouple wire errors Compensation error can arise from two sources inaccuracy of the temperature sensor and temperature differences between the sensor and the screw terminals The sensor on the SCB 68 board is specified to be accurate to 1 C You can minimize temperature differences between the sensor and the screw terminals by keeping the SCB 68 board away from drafts heaters and warm equipment SCB 68 Connector Block Installation Guide 12 National Instruments Corporation Thermocouple output voltages are nonlinear with respect to temperature Conversion of the voltage output to temperature using either look up tables or polynomial approximations introduces linearization error The linearization error is dependent on how closely the table or the polynomial approximates the true thermocouple output For example you can reduce your linearization error by using a higher degree polynomial Measurement error is the result of inaccuracies in the plug in board These inaccuracies include gain and offset If the board is properly calibrated the offset error should be zeroed out The only remaining error is a gain error of 0 08 of full range see the MIO 16 specifications If the input range is 10 V and the gain is 500 gain error contributes 0 0008 x 20 mV or 16 LV of error If the Seebeck
14. ial analog channel 0 to the temperature sensor by switching S5 and S4 to the up position as shown in Figure 4 Figure 4 Differential Switch Configuration e To disable the temperature sensor set switches S5 and S4 in the down position as shown in Figure 5 This is the factory default Figure 5 Disabled Temperature Sensor Switch Configuration SCB 68 Connector Block Installation Guide 4 National Instruments Corporation e For use with a 68 pin board you can bypass all of the circuitry using the switch configuration shown in Figure 6 Notice that when switches S1 S2 and S3 are set as shown in Figure 6 the temperature sensor and accessory power are off Figure 6 Switch Configuration for General Purpose Use with a 68 Pin Board Temperature Sensor Output and Accuracy The SCB 68 temperature sensor outputs 10 mV C and has an accuracy of 1 C You can determine the temperature using the following formulas T C 100 x Vt TCC Tx 273 15 where Tx is the temperature in Kelvin and Vt is the temperature sensor output voltage T C 9 43 miec 2 where T F and T C are the temperature readings in degrees Fahrenheit and degrees Celsius respectively Note Use the average of a large number of samples to obtain the most accurate reading Noisy environments require more samples for greater accuracy Fuse and Power One of the 5 V lines from the DAQ board pin 8 is protected by an 800 m
15. ntains the following components Kit Component Part Number SCB 68 68 pin shielded connector block 182470 01 SCB 68 Quick Reference Label 182509 01 SCB 68 68 Pin Shielded Connector Block Installation Guide 320745 01 If your kit is missing any components contact National Instruments Figure 1 shows how to remove the SCB 68 shielded connector block from its box Product and company names are trademarks or trade names of their respective companies 1994 National Instruments Corporation All rights reserved January 1994 Figure 1 shows how to remove the SCB 68 shielded connector block from its box Board Mounting Screws Grounding Flat Washer 68 Pin Connector Screws Washers Strain Relief A Shielding Screws Screws P Strain Relief Bars Figure 1 Removing SCB 68 Connector Block from Its Box SCB 68 Connector Block Installation Guide 2 National Instruments Corporation Figure 2 shows the SCB 68 board parts locator diagram R20 See fuse and Power Switches S3 S4 and S5 68 Pin 1 0 Connector RS oBego fol olio ao Be Pads for E oe Analog Input Conditionin g 00000000 1332222322222 el 000000000 I6600000000001 sf 0000000000 bs 0999000008 4 0000000000 IS Sooooo00000 1 4 0000000000 I3 1000000000048 0000000000 6400000000001 5 Os ea 0000000000 O RETR 130000000000049 0000000000 e 209998000997 7 0000000000 2890000900995 0000000000 ooo 89899890
16. supplies its own reference ground point and the MIO 16 should not supply one Therefore you should configure the MIO 16 board for nonreferenced single ended input mode In this configuration tie all of the signal grounds to AISENSE which connects to the negative input of the instrumentation amplifier on the MIO 16 board You can leave the SCB 68 inputs in the factory configuration that is with jumpers in the series position F or G depending on the channel Do not use the open positions that connect the input to AIGND A and C see Figure 7 in this configuration Therefore you should build signal conditioning circuitry requiring a ground reference in the custom breadboard area using AISENSE as the ground reference instead of building the circuitry in the open component positions Referencing the signal to AIGND can cause inaccurate measurements resulting from an incorrect ground reference Building RC Filters You can connect RC filters which can reduce noise to the SCB 68 analog inputs You can build single or differential RC filters using the pads on the SCB 68 Filtering increases settling time to the time constant of the filter you use Adding RC filters to scanning channels greatly reduces the scanning rate settling times can be 10 T T RC or longer Refer to Application Note 043 Measuring Temperature with Thermocouples National Instruments part number 340524 01 to determine if the settling time will affect your signal measurem
17. ting the wires into the green terminals and tightening the screws 6 Reinstall the strain relief bar if you removed it and tighten the strain relief screws 7 Close the top cover 8 Reinsert the shielding screws to ensure proper shielding You can now connect the terminal block to the 68 pin connector SCB 68 Connector Block Installation Guide 6 National Instruments Corporation Removing the SCB 68 Board To solder components in place you can remove the SCB 68 board using the following steps 1 Disconnect the 68 pin cable from the SCB 68 if it is connected 2 Remove the shielding screws on either side of the top cover with a Phillips head number 1 screwdriver You can now open the box Loosen the strain relief screws with a Phillips head number 2 screwdriver 3 4 Remove the signal wires from screw terminals 5 Remove the board mount screws and the 68 pin connector screws 6 Tilt the board up and pull it out To reinstall the SCB 68 board reverse the order of the steps Application Notes When you use the SCB 68 with the AT MIO 16X or MIO 16E Series boards you can use the 16 screw terminals for signal connection to the 16 analog inputs There is a breadboard area for these inputs to allow RC filtering 4 to 20 mA current sensing open thermocouple detection and an attenuator There are also pads for DACOOUT DACIOUT and EXTTRIG to permit RC filtering and an attenuator The open component positions on the SCB
18. to the time constant of the filter you use RC Filters You can build single RC filters using the pads R1 and RC1 for EXTTRIG R2 and RC2 for DACIOUT and R3 and RC3 for DACOOUT Solder the resistor in position R1 R2 or R3 and the capacitor in position RC1 RC2 or RC3 Determine your cutoff frequency and settling time using the following formulas Fe I 2 tRC Settling time 9 T for 12 bit DACs 12 T for 12 bit DACs Attenuators You can connect attenuators voltage dividers to the SCB 68 board Attenuators can reduce a signal that is outside the normal input range of the DAQ board 10 V maximum There is a two resistor circuit for attenuating voltages on the SCB 68 at DACOOUT DACIOUT and EXTTRIG Use pads R1 and RC1 for EXTTRIG R2 and RC2 for DACIOUT and R3 and RC3 for DACOOUT for the resistors You can determine the gain G of this attenuator using the following formula G RC1 RC1 R1 or G RC2 RC2 R2 or G RC3 RC3 R3 Warning The SCB 68 board is not designed for any input voltages greater than 42 V even if a user installed voltage divider reduces the voltage to within the input range of the DAQ board Input voltages greater than 42 V can damage the SCB 68 board any and all boards connected to it and the host computer Overvoltage can also cause an electric shock hazard for the operator National Instruments is NOT liable for damage or injury resulting from such misuse Sources of Error When making t
19. void dangerous electrical shock do not perform procedures involving cover or shield removal unless you are qualified to do so Before you remove the cover disconnect the AC power or any live circuit from the terminal block The chassis GND terminals on your terminal block are for grounding high impedance sources such as a floating source 1 mA maximum Do NOT use these terminals as safety earth grounds Do not connect high voltages to the SCB 68 even with an attenuator circuit Never connect voltages 242 Vrms National Instruments is NOT liable for any damages or injuries resulting from improper use or connection To connect the signal to the terminal block perform the following steps 1 Disconnect the 68 pin cable from the SCB 68 if it is connected 2 Remove the shielding screws on either side of the top cover with a Phillips head number 1 screwdriver see Figure 1 You can now open the box 3 Configure the switches and other options relative to the types of signals you are using as explained in the Switch Settings and Temperature Sensor Configuration section of this guide 4 Loosen the strain relief screws with a Phillips head number 2 screwdriver Slide the signal wires through the front panel strain relief opening You can also remove the top strain relief bar if you are connecting many signals Add insulation or padding if necessary 5 Connect the wires to the screw terminals by stripping off 0 25 in of the insulation inser
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